While boating is generally a safe sport, the fuels which power marine engines emit vapors that are potentially dangerous. Pleasure vessels typically have an internal combustion engine that is enclosed within an engine compartment to shield users from fumes and noise. However, inadequate ventilation of the engine compartment can result in an accumulation of combustible vapor. The mixture of vapor and air provides an explosive condition which can be ignited by the spark from an alternator or simply by a hot exhaust manifold or any unshielded electrical component. Every year, thousands of pleasure vessels undergo a fire or an explosion. Preventative devices are increasingly common, but the number of fires and explosions continues to increase each year.
A first hazardous time in which accumulated vapor is likely to explode is upon ignition of the engine. An inactive marine engine emits vapor which is more dense than air. The vapor accumulates at the bottom of an engine compartment. The U.S. Coast Guard requires installation of a ventilation system for inboard engine vessels, and recommends that the ventilation system be energized for a sufficient period of time prior to engine ignition so as to purge the engine compartment of combustible vapor. U.S. Pat. No. 4,473,025 to Elliott, U.S. Pat. No. 4,235,181 to Stickney, U.S. Pat. No. 3,951,091 to Doench, U.S. Pat. No. 3,948,202 to Yoshikawa, U.S. Pat. No. 3,675,034 to Abplanalp et al., U.S. Pat. No. 3,652,868 to Hunt and U.S. Pat. No. 3,489,912 to Hoffman, Jr. all teach blocking circuits for inboard engine ignitions which allow a blower to exhaust explosive fumes from an engine compartment prior to engine ignition.
A second potentially hazardous time is that time in which a marine vessel is idling, is decelerating, or is engaged at a low-cruise level. During such time, the engine operates on a richer fuel/air ratio and supplies a higher concentration of vapor. Moreover, because the marine vessel is either stopped or moving relatively slowly, there is little or no natural ventilation. Stickney includes a low-level ventilation actuation circuit which operates in response to detection of engine speed below a predetermined level. The speed circuit includes a speed sensor which may be connected to the ignition coil or distributor of an engine to output a signal having a frequency proportional to engine RPM. The signal is received by a one shot multivibrator which produces a pulse train having a pulse frequency directly proportional to engine RPM. This train of pulses is coupled to an integrator which operates to provide a voltage of a level directly proportional to the frequency of the multivibrator. The level of the voltage is compared to the level of a second voltage that is directly proportional to a preselected minimum engine RPM. If the actual engine RPM is below the minimum engine RPM, the ventilation system is actuated. As noted in the Stickney patent, the components of the speed circuit are different for different marine engines. The components are determined by the number of engine cylinders and the maximum engine RPM.
Engine startup and engine idling, or low cruise, are two of the more potentially hazardous times in which a vapor fire or explosion is likely to occur. However, fires and explosions may occur at any time. To explode, gasoline needs to be vaporized and mixed with air. The mixture can be caused by convection, evaporation, or a leak combined with the rocking motion of a marine vessel, as well as other reasons. The vapor/air mixture can thereafter be ignited by the spark from an alternator, or by a hot exhaust manifold, or by an unshielded electrical component.
U.S. Pat. No. 3,292,568 to Morrell teaches a protective device for boats. The device includes a delay circuit which prevents engine ignition for a predetermined period of time after closing of a boat ignition switch so that a blower can exhaust vapor during that time. The blower is also energized and the engine ignition circuit is deenergized if a detector senses a build-up of vapor during operation of the boat. The device further includes warnings of improper engine condition, identical to those warnings typically found in cars. For example, oil pressure and engine coolant temperatures are monitored.
Issued to the present applicant is U.S. Pat. No. 4,944,241, which teaches a marine safety system that offers an improvement to the Morrell device by adding a vacuum detection device connected to the intake manifold of a marine vessel. The detection device senses the potentially dangerous conditions of engine idling and low cruise and energizes a bilge blower accordingly. Thus, instead of restricting energization of the bilge blower to times in which it is also necessary to temporarily shut down operation of the engine, the marine safety system selectively initiates exhaustion to prevent vapor buildup during running of the engine. The marine safety system is also an improvement over the Stickney patent because the system can be used without adaptions for the number of engine cylinders and maximum RPM. However, the vacuum detection device of system is not as reliable when used with certain types of marine engines as it is with others. For example, two-cycle engines and turbocharged and supercharged engines are associated with intake manifold pressures which exceed atmospheric pressure. Such engines are often employed in diesel-fueled, ocean-going vessels.
It is an object of the present invention to provide a system for marine vessels which can be used with any type of marine engine.